Conventionally, in a bending apparatus such as a press brake, a plate-like work is bent to a desired predetermined angle using a punch and a die cooperatively.
For a bending process, a D value (stroke amount) is first established by “test” bending a work to a predetermined angle. The D value is the stroke amount that obtains the predetermined angle during the “test” bending.
The “test” bending includes a step of switching an NC control apparatus to a manual mode and thereafter driving a ram at a minute speed by a manual pulser. The driving of the ram is executed by an operator rotating a manual pulse handle to bend a work.
The D value is established as the stroke amount at a time when the predetermined angle, e.g., 90 degrees, is obtained during the test bending. After the D value is established, the D value is set to the NC control apparatus, and a continuous bending (a step of continuously bending multiple works) is executed as a “main bending” using the D value.
However, the predetermined angle cannot be reliably obtained in the main bending operation using the D value set to the NC control apparatus, for reasons explained herein. Accordingly, the angle obtained in main bending may be either too shallow or too deep when using the D value established during test bending.